ORIGIN OF SPINAL NERVES 



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A vertical line from the sixth thoracic to the third sacral spine will give the 

 spinal origin of the niuscle. Another from the third sacral spine to a ])oint on 

 the iliac crest, an inch or more outside the edge of the erector s)Mna', will give the 

 origin of the muscle from the sheatli of the erector spina? and the ilium. A line 

 from the sixth thoracic spine, almost transversely at first, with increasing slight 

 obliquity over the inferior angle of the scapula to the axilla and bicipital groove, 

 will mark the upper border of the nmscle. Another very oblicjue line from the 

 point on the iliac crest upwards and outwards to the axilla will give the lower 

 border and the tapering triangular apex of the insertion. The muscle may \w 

 attached to the angle of the scapula, or separated from it by a bursa. 



Fig. 708.— Relations of the Abdominal Visceka to the Antekiok Parietes. (Treves.) 



Triangle of Petit. — This small space lies above the crest of the ilium, at about 

 its centre, bounded by the anterior edge of the latissimus and the po.sterior border 

 of the external oblique. 



Origin of spinal nerves. — It is very inq)<)rtant to remember the relations of 

 these to the vertebral spines, in determining the results of disease or injury of the 

 cord and the parts thereby affected. The above relation may be given brietly as 

 follows : — 



The origins of the eight cervical nerves correspond to the cord between the occi- 

 put and the sixth cervical spine. The upper six thoracic come off lietween the 

 above spine and that of the fourth thoracic vertebra. The origins of the lower six 

 thoracic nerves correspond to the interval l)etween the fourth and the tenth thoracic 



